1. Field of the Invention
The present invention relates to an oscillation device, a detection device, and the like, of a semiconductor, for a terahertz waveband.
2. Description of the Related Art
In recent years, non-destructive sensing techniques using electromagnetic waves in a terahertz (THz) waveband (at frequencies of approximately 30 GHz to 30 THz) have been developed. Electromagnetic waves in such a frequency band allow applications in imaging techniques developed in the form of safe imaging and examining apparatuses without the use of X-rays. Other techniques that have been developed include spectroscopic techniques for obtaining the absorption spectrum and the complex permittivity of a substance to determine its properties such as molecular bonding, measurement techniques for determining properties such as carrier density and mobility, conductivity, and the like, and analytic techniques for biomolecules. Additionally, the IEEE802.15 THz Interest Group has been active in the development of wide-band wireless communications using THz waves as carrier waves.
Light sources for such THz waves have been developed using nonlinear phenomena through laser excitation or using photoconductivity of semiconductors. Microwave-band oscillators that multiply waves are also used. However, they all suffer difficulty in improving the efficiency of generating THz waves and have complex configurations, and thus there is demand for semiconductor chips that can be driven electrically. One such oscillator is a resonant tunneling diode (RTD) device (see IEEE Microwave and Guided wave letters, vol. 5, p. 219, 1995.). This device, through electromagnetic wave gain due to the negative resistance of the RTD and the integration of a resonator that also works as an electromagnetic wave emitter, provides oscillation output in a terahertz waveband with voltage application at room temperatures.
Other attempts include integrating such a device having the negative resistance with a transistor device for amplification and mixing of the oscillation output to thereby improve the performance of space transmission by high frequency electromagnetic waves (Japanese Patent Application Laid-Open No. 2005-142476).
An HEMT (high electron mobility transistor) device provided with grating electrode gates has been disclosed as one type of high speed transistor (see Japanese Patent Application Laid-Open No. 2009-224467). In this device, the frequency of a plasmon occurred in a two-dimensional electron gas region is adjusted through the grating electrode gates. External rays of light with two wavelengths are allowed to enter the device, and the beat frequency is tuned in the resonance frequency of the plasmon to generate THz waves.
An RTD oscillator necessitates the integration of a shunt resistor and a MIM capacitor in proximity to an RTD device to oscillate at a desired oscillation frequency. Depending on the structure of a resonator required for the oscillator, there may be problems as described below. That is, the structural size may be limited for obtaining a resistance value required for the integrated-type shunt resistor, and the application of a modulation signal from an external power source may impose an upper limit of approximately 10 GHz by the MIM capacitor required to prevent parasitic oscillation. Note that this calculation assumes a modulation bandwidth of 3 db down, MIM capacitance of 10 pF, and wiring resistance slightly less than 1Ω.
By integrating this type of oscillator with a transistor as described in Japanese Patent Application Laid-Open No. 2005-142476 to obtain an amplifying function, the transistor may provide a modulating function to alleviate the problems described above. Fabricating such an integrated circuit for a terahertz region, however, may require highly accurate shape control, making it difficult to obtain a high yield.